Engine bearings of this type have been generally known in the state of the art and are preferably intended for mounting the internal combustion engine of a motor vehicle and to prevent disturbing vibrations from being transmitted from the engine to the body.
Disturbing vibrations of essentially two types, caused by the engine, occur during the operation of the vehicle and they therefore require different stiffnesses of the engine bearings used for the vibration damping. To embody the different damping characteristics, hydraulically damped engine bearings can be used, in which a second spring element is connected in parallel or in series to the first spring element, which is designed, e.g., as a conventional rubber bearing. If the spring action of the two spring elements connected in series is effective, the overall stiffness of the engine bearing is lower than the individual spring stiffness of the two spring elements used. If such an engine bearing is blocked by means of a corresponding switching device, this means that the flux of force flowing through the engine bearing flows only over one spring element, whose stiffness alone is effective and is substantially higher than when both spring elements are effective at the same time.
Various possible embodiments for blocking one ofthe spring elements have been known in the state of the art. For example, DE 41 30 362 discloses an engine bearing comprising two elastomeric spring elements, in which one spring element is blocked by means of a hydraulically pressurized pressure pad such that two housing elements, which enclose the spring element to be blocked between them, are brought into contact with one another in a non-positive manner by pumping up the pressure pad. This type of blocking of a spring element has the drawback that an external hydraulic energy source, which requires a relatively large installation space with the corresponding connection lines to the engine bearing and whose installation is also labor-intensive and expensive, is always necessary for such engine bearings.
The above-mentioned prior-art document also discloses the possibility of embodying the blocking of a spring element by a motor operator with a pressure piston which is actuated by same. Two support plates are brought into non-positive contact with one another by the motor operator with the pressure piston, so that the second spring element in the form of a rubber body is thus bridged over and is put out of operation.
Since the motor operator moves the piston for blocking the second spring element by means of a screw spindle, the axial and radial forces that can be transmitted are limited in this exemplary embodiment or the switching means occupies a rather substantial mounting space because of it being dimensioned for stronger forces, which in turn limits the use of the entire engine bearing.
Moreover, DE 34 03 002 discloses an engine bearing which is based on the cooperation of two spring elements with different spring characteristics and a switching coupling. The switching coupling, which can be actuated electromagnetically, is connected in series with the relatively harder spring element. The switching coupling is used to compress a disk packet by magnetic forces in the switched-on state in order to thus establish a rigid connection between the first spring element and the supporting element, so that the second spring element is put out of operation. The transmission of axial and radial forces is limited in this engine bearing as well because of the friction forces to be applied between the individual disks of the switching coupling, which can be compensated by a bulkier design in certain ranges, but these engine bearings are, on the whole, disadvantageous because of their size and weight.